docs: def add_contact(self, segment_id, contact_id):
          """
          Add a contact to the segment
  
          :param segment_id: int Segment ID
          :param contact_id: int Contact ID
          :return: dict|str
          """
  
          response = self._client.session.post(
              '{url}/{segment_id}/contact/add/{contact_id}'.format(
                  url=self.endpoint_url,
                  segment_id=segment_id,
                  contact_id=contact_id
              )
          )
          return self.process_response(response)